The present invention provides novel antibiotic resistance-conferring cloning vectors for use in Escherichia coli, Streptomyces, and Actinomadura. In the prior art the introduction, development, and exploitation of recombinant DNA technology in the latter two classes of microorganisms has been difficult, because of the absence of selectable genetic markers on cloning vectors. This has been a particular problem in the Actinomadura especially because few if any plasmid vectors have heretofore been available. The vectors in the present invention may be obtained in Escherichia coli, Streptomyces, and Actinomadura and therefore, represent a significant advance in the art. In addition these vectors are functional in all of these classes.
The present vectors are experimentally convenient and useful, because of their small size, cross-genus transformability, and ability to transform and be selected from any restrictionless species of Streptomyces or Actinomadura strain that is sensitive to thiostrepton. This particular drug is an excellent selective agent due to the widespread sensitivity among the Actinomycetales, its stability upon prolonged incubation, and the simple mechanism of resistance, namely a 23S ribosomal RNA methylation conferring high-level resistance due to target site modification.